AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 1 132-R138, Copyright © 1993 by American Physiological Society
Effects of capsaicin on micturition and associated reflexes in rats
C. L. Cheng, C. P. Ma and W. C. de Groat
Department of Pharmacology, University of Pittsburgh, Pennsylvania 15261.
The effect of capsaicin on micturition and associated reflexes was studied
in urethan-anesthetized female rats. Capsaicin or vehicle solution were
administered 4 days before the experiment in a dose of 125 mg/kg sc or
during the experiment in a dose of 50-100 mg/kg sc. Activity of the urinary
bladder was recorded by measuring intravesical pressure via a urethral
catheter while slowly filling (0.052 ml/min) the bladder or when the
bladder was distended beyond the micturition threshold and maintained at a
constant volume. Pretreatment with capsaicin did not significantly change
various parameters of urinary bladder function including micturition volume
threshold or the amplitude, duration, and interval between reflex bladder
contractions. However, capsaicin pretreatment significantly reduced (80%
decrease) the arterial pressor responses accompanying reflex bladder
contractions and reduced by approximately one-half the percentage of
animals in which bladder activity was inhibited by stimulation of the
uterine cervix. A large dose of capsaicin (50 mg/kg sc) elicited an acute
block of bladder activity that persisted for 8-15 h. This effect is
attributable to an action on myelinated afferent or efferent components of
the micturition reflex pathway. It is concluded that capsaicin-sensitive
afferents are not essential for the performance of micturition in the rat.
However, these afferents are involved in cervicovesical reflex mechanisms
that modulate bladder activity and in vascular reflexes triggered by
isometric bladder contractions.
